GST 2.0 slabs 0% · 5% · 18% · 40% from 22 Sep 2025Special rates 0.25% & 3% stones · precious metalsLate fee ₹50/day ₹20/day for nil returnsLate-fee cap ₹2,000 – ₹10,000 by turnoverInterest 18% p.a. on tax paid lateIntra-state CGST + SGST split equallyInter-state IGST full rateGSTIN 15 characters with a check digitGST 2.0 slabs 0% · 5% · 18% · 40% from 22 Sep 2025Special rates 0.25% & 3% stones · precious metalsLate fee ₹50/day ₹20/day for nil returnsLate-fee cap ₹2,000 – ₹10,000 by turnoverInterest 18% p.a. on tax paid lateIntra-state CGST + SGST split equallyInter-state IGST full rateGSTIN 15 characters with a check digit
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GST calculators

🧮GST CalculatorAdd or remove GST with the CGST, SGST or IGST split.🔄Reverse GST CalculatorFind the base price and tax inside a GST-inclusive amount.⏰GST Late Fee & Interest CalculatorLate fee and 18% interest for a delayed GSTR-3B or GSTR-1.📈GST Profit Margin CalculatorCost price to selling price with margin, GST and cess.🔎GSTIN ValidatorCheck a GSTIN’s format, checksum, state and PAN.

Invoices & billing

🧾GST Invoice GeneratorA GST-ready tax invoice with auto totals, saved as PDF.📋Quotation MakerProfessional GST quotations with logo, bank details and terms.📒Billbook ToolBills, party book, numbering and balance tracking on your device.

GST guides

📘GST 2.0 explainedThe 5%, 18% and 40% slabs and what changed.📘How to calculate GSTAdd and remove GST formulas with examples.📘CGST vs SGST vs IGSTWhich tax applies within and across states.📘GST invoice rulesMandatory fields, copies and time limits.📘Quotation vs invoice vs proformaWhen to use each document.
All 8 tools are free, need no sign-up and run in your browser.Who builds bydigital →
Home › Mantu Kumar

Mantu Kumar

Founder and editor of bydigital GST tools.

Mantu Kumar

Founder and editor of bydigital. Builds and checks every GST calculator and billing tool on the site, from Navi Mumbai, India.

[email protected] · Profile updated 25 October 2026

What Mantu does at bydigital

Mantu Kumar started bydigital to answer everyday GST questions without accounting software: adding or removing GST, splitting CGST, SGST and IGST, estimating a late fee, pricing a product with margin and tax, and producing a clean invoice or quotation in a minute. He chooses which tools to build, writes the code and the guides, and is responsible for every number the site shows.

He also builds other free browser-based tools, including TradeProfy (trading cost calculators), QuickCVLab (CV builder) and LyfPDF (PDF tools), on the same principles: no sign-up, nothing uploaded, and an honest explanation of each result.

How he checks a GST tool

  1. Start from the rule. Rates come from GST Council decisions as notified by CBIC; late fees from Section 47 of the CGST Act and the capping notifications; interest from Section 50; the GSTIN check digit from the published algorithm.
  2. Work examples by hand. Every tool is tested with cases worked out manually, including edge cases such as nil returns, custom rates and inter-state supplies.
  3. Say what the tool cannot do. Each page states its limits: a GSTIN check proves the format, not live registration; a late-fee estimate does not include waivers announced later.
  4. Review after changes. When the GST Council changes a rate or a cap, the tools, guides and examples are updated together and the review date changes.

What he does not claim

Mantu is not a chartered accountant, tax practitioner or lawyer, and bydigital does not present him as one. The tools give estimates and templates. For filing decisions, notices or classification, consult a CA or the official portal.

Topics he writes about

  • GST calculation, inclusive and exclusive prices
  • CGST, SGST, IGST and place of supply
  • Late fees and interest on GST returns
  • GST invoices, quotations and billing
  • GSTIN structure and validation

Guides by Mantu Kumar